Solenoids

A solenoid is basically an electric coil. When a battery is connected to the coil a magnetic field is created and pulls a plunger back. This then opens a valve allowing high-pressure air to flow into the pneumatic cylinder. When the battery is disconnected the plunger is pushed back, closing the valve and blocking the flow of high-pressure air while letting air flow out of the cylinder. The most common type of solenoid acts as a linear actuator that retracts when an electric current is applied, if the current is maintained the solenoid will continue to apply force and it only returns to its extended state if a spring or a force is applied.